It's important to remember the 9/11 attacks and to honor those who were lost, but it's also important to remember that the war with terrorism has never ended, Rep. Pete King said Monday.

"It is a day none of us should forget," the New York Republican told Fox News' "America's Newsroom" program. "I lost many friends and neighbors that day. It's important that we honor the memory of those who died and stay in contact with their families and just as importantly we have to remember this war goes on. We can never let our guard down."

The United States is "much safer" than it was 16 years ago, "but the threat is greater," said King. "They're constantly attempting to find ways to attack us. We can't let our guard down."

The five remaining 9/11 suspects remain at the internment center in Guantanamo Bay, Cuba, with a trial date expected in 2019, nearly 20 years after the attacks occurred.

"It's important they be detained and important we have the trials," King said. "They have to be brought to justice. I think there has been too many delays. Too many people seem more interested in what they perceive to be civil rights of those who killed innocent Americans, but we are going to persevere."

The trials are owed to those who lost their lives in the 2001 attacks, he continued, and also, the United States owes a signal to the world that it "won't be intimidated by political correctness or against Islamist terrorism."

The threat of such terrorism has grown drastically since the 9/11 attacks, said King.

"Back on 9/11 you were talking about one enemy force, al-Qaida, in a few caves in Afghanistan," said King. "It is now a worldwide movement. Al-Qaida, ISIS, Boko Haram, a list of Islamist terrorist groups that morphed from al-Qaida."

The groups are on the run, but the United States must keep up its pressure, King said.

"I'm not trying to say this in a partisan way, but I think with the Obama administration, too often we backed away or we didn't want to . . . in some ways we were very aggressive, but others apologetic," King said. "We can't be. We have to stay on offense all the time, kill them before they kill us and there is a threat in the United States."

The United States has to win based on pushing back, both militarily and through intelligence measures, said King.

"We need to find leaders in the Muslim world who are willing to stand with us and be very forceful and not apologetic themselves," King said. "It will be a long, hard fight."

In the months after the 9/11 attacks, there was "tremendous unity" in the United States, but since then, the United States has become divided again, he continued.

"The enemy is united," King said. "If anything good did come from 9/11, it was tremendous unity. I always hope when we recall the attacks we can get back some of that spirit realizing how much we have in common."

King said he would also like for the government to be sure that the FBI and other law enforcement agencies have everything they need to protect the United States.

"Because of political correctness they're not kept from doing the job they have to do, to detect and find those in our society, the bombers or others who attempt to destroy us from within and also to give our military leaders all the power and authority they need to destroy ISIS and al-Qaida and all those affiliates overseas," King said.

King recalled that he was in a car heading to Washington on the day of the attack, and immediately worried about his wife, who was on the runway at LaGuardia on the day of the attack.

"I was wondering, was that her plane?" King said. "I had no way of making contact with her. My son worked in the Commerce Department. There was a rumor a bomb had gone off there. I was thinking personally for the first half hour. After an hour, I realized they were safe then it suddenly hit me wait, there are thousands of people in that building and all day long I got calls from friends and family and friends and neighbors who were killed and it became one horrific period of days and weeks and months of wakes and funerals, memorial services and also being in Washington trying to get our defenses up."